Electric vehicles are propelled by an electric drivetrain powered by an electrochemical battery as an energy storage device. Range extended electric vehicles (serial hybrid) are propelled by an electric drivetrain powered by an electrochemical battery which is recharged by a small internal combustion engine (ICE) such as a generator to extend vehicle range when the energy in the storage device becomes sufficiently depleted.
Electric vehicle performance is inherently sensitive to vehicle mass, energy efficiency, component weight, parasitic loads, power management, thermal and solar loads; all of which are well known and can be accounted for during vehicle design.
An SAE paper 2012-01-0651 “Fuel Consumption Simulation Model for Transit Buses Based on Real Operating Condition to Assist Bus Electrification” found that the operating fuel economy of (Winnipeg, Manitoba Canada) transit buses depended on a number of factors, including the fuel consumption characteristics of the engine, transmission characteristics, weight of the vehicle (which varies with passenger load changes), aerodynamic resistance, rolling resistance of the tires, driving cycle conditions, and driver behavior.
When a transit bus pulls into a bus stop passengers typically will disembark and embark the vehicle. At every bus stop, the passenger load changes along with the vehicle power requirements. The maximum passenger load recorded during the study was 89 with a minimum of zero, and the average passenger load was 12. Passenger load variations in this case affected the vehicle mass by 5785 kg or 89 passengers at an assumed weight of 68 kg per passenger. For example, the New Flyer D40LF transit bus from the study has a curb weight of 12,301 kg and when fully loaded with 89 passengers, weighs 18,086 kg.
A transit bus propulsion system is sized to provide sufficient power to enable the bus to meet the performance requirements defined by the American Public Transportation Association (APTA) for acceleration, top speed, route, Gross Vehicle Weight Rating (GVWR) and gradeability requirements and to operate all accessories as needed. A transit bus must also be capable of achieving a specified top speed within a given amount of time; 50 mph (80 kph) within 60 seconds on a straight, level road at GVWR, with all accessories operating.
Transit bus minimum gradeability requirements are also well defined. For instance, the propulsion system and drivetrain shall enable the bus to achieve and maintain a speed of 40 mph (64 kph) on a 2½ percent ascending grade and 15 mph (24 kph) on a 10 percent ascending grade continuous over a distance of 2/10 of a mile. Because transit bus performance at GVWR has been defined by APTA you now only have to determine the motor power requirements, which is dependent on the bus characteristics and can be determined by using basic Newtonian mechanics.
An electric transit bus propulsion system should also be equipped with regenerative braking capability, and the braking effort it develops should blend with and augment the vehicle brakes in order to maximize the life of the wearing components in the braking system. The regeneration system should be programmable to allow optimization of the vehicles deceleration and regeneration rate. Actuation of the Anti-lock Braking System (ABS) and/or Anti-Slip Regulation (ASR) must override the operation of the regenerative braking.
The regeneration braking shall become partially engaged with a resulting deceleration of no greater than (0.07 g) when the throttle pedal is completely released. The maximum regeneration rate shall be achieved when brake pedal is depressed prior to engagement of the service brakes, with a maximum resulting deceleration of approximately 0.20 g (APTA) in an empty bus. The resulting decelerations specified include the effects of aero dynamic and rolling resistance. The Canadian Transit Handbook (Canadian Urban Transit Association and Transportation Association of Canada) suggests the desirable Deceleration Rate (normal service) for a standard bus of 1.1(m/s2) or 0.112 g.
The (Winnipeg, Manitoba Canada) study above “SAE paper 2012-01-065” shows passenger load variations affected the vehicle mass by up to 5785 kg. As vehicle mass increases, the resulting lower deceleration rate upon regenerative braking onset correspondingly decreases the rate of return over the same time period the vehicles kinetic energy to the energy storage device from regenerative braking and the overall energy efficiency of the vehicle.
It is typical to have to stop the vehicle in a given distance from the time braking is commenced. In such situations it increases power conservation and consumption efficiency to increase the amount of regenerative braking in proportion to the amount of vehicle mass increase. As vehicle mass is increased it takes more power kW to accelerate the vehicle at the same rate of the lower mass. There is a maximum resulting deceleration of approximately 0.20 g in an empty bus. The deceleration rate will be lower for a fully loaded bus (it takes more energy to slow down) so the vehicle brakes would have to be applied more to maintain the maximum deceleration rate of an empty bus. As the present system continually monitors the gross mass of the vehicle, the system can increase the regeneration rate to maintain the 0.2 g for its increased mass or (X) deceleration rate and increase the amount of energy going back into the battery pack by increasing the regeneration rate and use the vehicle brakes less.
If APTA had set the deceleration rate of 0.2 g in braking a fully loaded bus, it would throw standing passengers off their feet in a lightly loaded bus. The APTA intent was to limit the “Jerk” at retarder or regeneration onset because the only known mass is the empty vehicle.
Once vehicle mass, and road grade and accessory loads become factors used to regulate the amount of power supplied to electric vehicles, vehicle driver performance remains as the sole unknown variable linked to electric vehicle range. Vehicle speed and acceleration are closely related to energy consumption in all electric vehicles. Electric vehicle range depends heavily on driving habits (aggressive vs. smooth acceleration).
For example, driver aggressiveness and its effect on driving range:                0.04 g average acceleration=120 km range        0.08 g average acceleration=80 km range        
Adaptive power control systems found in the prior art are used primarily with parallel hybrid electric/ICE vehicle designs, but they do not optimize the performance of full electric vehicle power systems or electric batteries supplemented by generators (serial electric). In full electric configurations, unburdened by the weight and complexity of full sized ICE's, the maximum potential of electric vehicle power can be realized, but only if the key variables are managed appropriately, such as driver performance, regenerative braking, vehicle mass, road grade, etc. An Electric Vehicle Power Management System and Driver Control method is needed to both efficiently manage power use and minimize speedy and aggressive driving profiles, thereby maximizing vehicle driving range across a broad spectrum of drivers and conditions typically found in transit bus and freight delivery operations.